The invention relates to a method for controlling an internal combustion engine, having intermittently actuated inlet valves, in which in each case fuel is introduced into a combustion chamber and a combustion air mass flow (MF) flowing into the combustion chamber through an intake tract is set, whereby a pressure is determined in the intake tract and two final control elements, which influence the air mass flow in each case, connected in series in the intake tract are used for setting the air mass flow.
In particular in the case of an internal combustion engine having external fuel/air mixing a method is known for controlling the combustion air mass flow and thus the fuel injection in the combustion chambers by way of a final control element provided in the intake tract. Normally this final control element takes the form of a throttle valve which can be used to stop the cross-section of the intake tract. The position of the throttle valve then has a direct effect on the fuel injection. If the throttle valve is not fully open, then the air drawn in by the internal combustion engine is throttled and the torque delivered by the internal combustion engine is thus reduced. This throttle effect depends on the position and thus on the cross-section of opening of the throttle valve. When the throttle valve is fully open, the maximum torque is delivered by the internal combustion engine.
In order to achieve optimum control of the throttle valve, the latter is actuated by an actuator with position feedback. In this situation, a control unit is provided which calculates the required opening for the throttle valve by taking into consideration the current operational state of the internal combustion engine and controls the throttle valve actuator. To this end, an accelerator pedal position is evaluated by way of a pedal sensor.
During operation of the internal combustion engine, particular importance is attached to the determination of the air mass flowing into the combustion chambers of the internal combustion engine. EP 0 820 559 B1 proposes a model-based method in this respect, in which a variable which is characteristic of the fuel injection, namely the air mass flow or induction manifold pressure, is measured and used in a model structure for more precise determination of the fuel injection. As a result, it is possible to exactly implement a desired fuel injection, which has been calculated from a requested torque for example, by means of a corresponding throttle valve setting.
In order to keep the losses occurring at the throttle valve as small as possible, a method is known whereby the inlet valves are capable of being operated with variable valve lift as a second final control element in the intake tract. The inlet valves then open with an adjustable valve lift such that it is possible to dispense with the effect of the throttle valve at least in certain operational phases of the internal combustion engine. The fuel injection for the internal combustion engine is then controlled exclusively by way of the valve lift setting.
In the case of internal combustion engines employing a fuel/air mixture intake, the mixture is formed outside the combustion chamber. For example, an individual injection system is provided in which each combustion chamber of a multi-cylinder internal combustion engine is assigned one injection valve which introduces fuel immediately before the inlet valve. This enables control to be exercised in such a manner that the appropriate fuel mass is allocated to each combustion chamber. By injecting a precisely metered fuel mass immediately before the inlet valve, the mixture formation is improved and an undesired wetting of the walls of the intake tract is avoided.
However, in order to be able to ascertain the appropriate fuel mass, it is necessary to take the combustion air quantity into consideration.
This applies not only to systems where the fuel/air mixture is formed externally but also in the case of internal mixture formation, in other words where fuel is introduced directly into combustion chambers of an internal combustion engine.